Redox Reactions between Mn(II) and Hexagonal Birnessite Change Its Layer Symmetry

TY - JOUR

T1 - Redox Reactions between Mn(II) and Hexagonal Birnessite Change Its Layer Symmetry

AU - Zhao, Huaiyan

AU - Zhu, Mengqiang

AU - Li, Wei

AU - Elzinga, Evert J.

AU - Villalobos, Mario

AU - Liu, Fan

AU - Zhang, Jing

AU - Feng, Xionghan

AU - Sparks, Donald L.

N1 - Funding Information: The authors thank the National Natural Science Foundation of China (Grant Nos. 41471194 and 41271253) and the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB15020402) for financial support of this research. M.Z. is grateful for the support from the U.S. National Science Foundation under Grant No. EAR-1529937. We gratefully acknowledge the associate editor Dr. Daniel Giammar and the five anonymous reviewers for their constructive comments on the manuscript. Publisher Copyright: © 2016 American Chemical Society.

PY - 2016/2/16

Y1 - 2016/2/16

N2 - Birnessite, a phyllomanganate and the most common type of Mn oxide, affects the fate and transport of numerous contaminants and nutrients in nature. Birnessite exhibits hexagonal (HexLayBir) or orthogonal (OrthLayBir) layer symmetry. The two types of birnessite contain contrasting content of layer vacancies and Mn(III), and accordingly have different sorption and oxidation abilities. OrthLayBir can transform to HexLayBir, but it is still vaguely understood if and how the reverse transformation occurs. Here, we show that HexLayBir (e.g., δ-MnO2 and acid birnessite) transforms to OrthLayBir after reaction with aqueous Mn(II) at low Mn(II)/Mn (in HexLayBir) molar ratios (5-24%) and pH ≥ 8. The transformation is promoted by higher pH values, as well as smaller particle size, and/or greater stacking disorder of HexLayBir. The transformation is ascribed to Mn(III) formation via the comproportionation reaction between Mn(II) adsorbed on vacant sites and the surrounding layer Mn(IV), and the subsequent migration of the Mn(III) into the vacancies with an ordered distribution in the birnessite layers. This study indicates that aqueous Mn(II) and pH are critical environmental factors controlling birnessite layer structure and reactivity in the environment.

AB - Birnessite, a phyllomanganate and the most common type of Mn oxide, affects the fate and transport of numerous contaminants and nutrients in nature. Birnessite exhibits hexagonal (HexLayBir) or orthogonal (OrthLayBir) layer symmetry. The two types of birnessite contain contrasting content of layer vacancies and Mn(III), and accordingly have different sorption and oxidation abilities. OrthLayBir can transform to HexLayBir, but it is still vaguely understood if and how the reverse transformation occurs. Here, we show that HexLayBir (e.g., δ-MnO2 and acid birnessite) transforms to OrthLayBir after reaction with aqueous Mn(II) at low Mn(II)/Mn (in HexLayBir) molar ratios (5-24%) and pH ≥ 8. The transformation is promoted by higher pH values, as well as smaller particle size, and/or greater stacking disorder of HexLayBir. The transformation is ascribed to Mn(III) formation via the comproportionation reaction between Mn(II) adsorbed on vacant sites and the surrounding layer Mn(IV), and the subsequent migration of the Mn(III) into the vacancies with an ordered distribution in the birnessite layers. This study indicates that aqueous Mn(II) and pH are critical environmental factors controlling birnessite layer structure and reactivity in the environment.

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U2 - https://doi.org/10.1021/acs.est.5b04436

DO - https://doi.org/10.1021/acs.est.5b04436

M3 - Article

C2 - 26745815

SN - 0013-936X

VL - 50

SP - 1750

EP - 1758

JO - ES and T Contents

JF - ES and T Contents

IS - 4

ER -